On the Ratio of Facular Area to Sunspot Area

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Session 123 -- Solar Magnetic Field and Solar Variabilty
Oral presentation, Thursday, 12, 1995, 2:00pm - 3:30pm

[123.05] On the Ratio of Facular Area to Sunspot Area

G.A. Chapman, A.M. Cookson, and J.J. Dobias (SFO/CSUN)

The ratio of the area of faculae (or network) to the area of sunspots is an important issue when discussing the energy balance within solar active regions. It is also of importance for the variability of solar-type stars. We have studied the ratio of facular to sunspot area for several years of photometric data from the San Fernando Observatory. The data are from full disk photometric images obtained with the CFDT1 (Cartesian Full Disk Telescope, 5" pixels). The sunspot corrected area is determined from a red image (672.3 nm, bandpass = 10 nm) and the corrected facular area is from a K-line image (393 nm, bandpass = 1 nm). The facular and sunspot areas are from the entire disk without regard to location or association with active regions. We carried out a regression of the following form: $$ A_F = a + b A_S + c A_S^2 $$ where $A_F$ is the corrected facular area and $A_S$ is the corrected sunspot area. We find the following:

\begin{tabular}{ccccccc} period &$a$ &$\sigma_a$ &$b$ &$\sigma_b$ &$c$ &$\sigma_c$ \\ 1989 &19,819 &7,047 &6.89 &1.6 &-0.00074 &0.00033 \\ 10/1/91 to \\ 12/31/92 &10,274 &5,904 &10.1 &1.48 &-0.0014 &0.00044 \\ \end{tabular}

The value of a and $\sigma_a$ are in micro-hemispheres. The negative sign for the coefficient $c$ indicates that increase in facular area does not keep pace with the increase in spot area for large spots. However, at no point does the slope go negative. These results are preliminary, as the latest reduction software has not been used. Results for 1990, 1991 and 1993 should be available by the time of the meeting. We find that the ratio of facular to sunspot area is approximately 10 but the detailed fit varies with the solar cycle. There is a significant quadratic term but much smaller than that found by Foukal (1994). This research was supported in part by grants NSF ATM-9115111 and NASA NAGW-3017.

Reference Foukal, P. 1994, Science 264 , 238.

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